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Rear axle ratio question

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The 3.98 is a lower gear, I had that in a truck & it did good pulling dump trailer. I think the 3.79 would be fine in a tractor, idk about a straight dump.

truck had mp8 with 505hp. 

Edited by 1965
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Depending on exactly which 13 Fuller is being used, the 3.98 ratio will be better for you. 

Let's say your Fuller has the 13.13 1st gear ratio, as many do, combined with the 3.98 rear end will give an overall ratio of 52.25. 

A Mack X107 6 speed (lo hole) has a first gear ratio of 14.10 combined with a 4.17 rear (pretty common ratio) gives ratio of 58.97 and they play pretty well off road.  Camelback suspension helps also in the dirt.

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It doesn't cost anything to pay attention.

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If I  understand this correctly you want a double over drive box on 3.79 or 3.98 and you want to pull 30 - 35 tons

Unless its down hill and the load is very flat, as in sheet steel I doubt it would be very practical 

Or maybe you have 700 hp and 3000 pounds of torque 

Working gearing out on paper is a lot different than using it everyday

I feel I would get sick of changing gears pretty quick and would much prefer to have the revs up a bit and just keep on poking along for a extra 1/4 of a hour each day

Cummins used to have really good formulas for working this out and it took into account the height, the like terrain and the speed you wanted to travel at

Im sure there must be some program or formula still out there to work this out 




Edited by mrsmackpaul
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my pete had 3.90  with an 18 spd and 550 cat. never once had a problem with local dump work, but a lot of that is the motor also  my 12 mack had 3.55 and 13 spd  with 445 mp8.  never had a problem, but i've also done this for 20 years and keep out of most situations where i'll break something or get stuck too bad. 3.79 or 3.70 would be right between my two, they would be fine.  3.98 might be a little slow on the highway

Edited by Nobody454
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